1WAIT(2) System Calls Manual WAIT(2)
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6 wait, waitpid, wait4, wait3 - wait for process terminatation
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9 #include <sys/types.h>
10 #include <sys/wait.h>
11 pid = wait(status)
13 int pid;
14 union wait *status;
15 #include <sys/time.h>
17 #include <sys/resource.h>
18 pid = waitpid(wpid, status, options);
20 int pid;
21 int wpid;
22 union wait *status;
23 int options;
24 pid = wait3(status, options, rusage);
26 int pid;
27 union wait *status;
28 int options;
29 struct rusage *rusage;
30 pid = wait4(wpid, status, options, rusage);
32 int pid;
33 int wpid;
34 union wait *status;
35 int options;
36 struct rusage *rusage;
37
39 The wait function suspends execution of its calling process until sta‐
40 tus information is available for a terminated child process, or a sig‐
41 nal is received. On return from a successful wait call, the status
42 area contains termination information about the process that exited as
43 defined below.
44 The wait4 call provides a more general interface for programs that need
46 to wait for certain child processes, that need resource utilization
47 statistics accummulated by child processes, or that require options.
48 The other wait functions are implemented using wait4 .
49 The wpid parameter specifies the set of child processes for which to
51 wait. If wpid is -1, the call waits for any child process. If wpid is
52 0, the call waits for any child process in the process group of the
53 caller. If wpid is greater than zero, the call waits for the process
54 with process id wpid . If wpid is less than -1, the call waits for any
55 process whose process group id equals the absolute value of wpid .
56 The status parameter is defined below. The options parameter contains
58 the bitwise OR of any of the following options. The WNOHANG option is
59 used to indicate that the call should not block if there are no pro‐
60 cesses that wish to report status. If the WUNTRACED option is set,
61 children of the current process that are stopped due to a SIGTTIN ,
62 SIGTTOU , SIGTSTP , or SIGSTOP signal also have their status reported.
63 If rusage is non-zero, a summary of the resources used by the termi‐
65 nated process and all its children is returned (this information is
66 currently not available for stopped processes).
67 When the WNOHANG option is specified and no processes wish to report
69 status, wait4 returns a process id of 0.
70 The waitpid call is identical to wait4 with an rusage value of zero.
72 The older wait3 call is the same as wait4 with a wpid value of -1.
73 The following macros may be used to test the manner of exit of the
75 process. One of the first three macros will evaluate to a non-zero
76 (true) value:
77 WIFEXITED(status) - True if the process terminated normally by a call
79 to _exit(2) or exit(2) .
80 WIFSIGNALED(status) - True if the process terminated due to receipt of
82 a signal.
83 WIFSTOPPED(status) - True if the process has not terminated, but has
85 stopped and can be restarted. This macro can be true only if the wait
86 call specified the WUNTRACED option or if the child process is being
87 traced (see ptrace(2)).
88 Depending on the values of those macros, the following macros produce
90 the remaining status information about the child process:
91 WEXITSTATUS(status) - If WIFEXITED(status) is true, evaluates to the
93 low-order 8 bits of the argument passed to _exit(2) or exit(2) by the
94 child.
95 WTERMSIG(status) - If WIFSIGNALED(status) is true, evaluates to the
97 number of the signal that caused the termination of the process.
98 WCOREDUMP(status) If WIFSIGNALED(status) is true, evaluates as true if
100 the termination of the process was accompanied by the creation of a
101 core file containing an image of the process when the signal was
102 received.
103 WSTOPSIG(status) If WIFSTOPPED(status) is true, evaluates to the number
105 of the signal that caused the process to stop.
106
108 See sigvec(2) for a list of termination signals. A status of 0 indi‐
109 cates normal termination.
110 If a parent process terminates without waiting for all of its child
112 processes to terminate, the remaining child processes are assigned the
113 parent process 1 ID (the init process ID).
114 If a signal is caught while any of the wait calls is pending, the call
116 may be interrupted or restarted when the signal-catching routine
117 returns, depending on the options in effect for the signal; see
118 intro(2), System call restart.
119
121 If wait() returns due to a stopped or terminated child process, the
122 process ID of the child is returned to the calling process. Otherwise,
123 a value of -1 is returned and errno is set to indicate the error.
124 If wait4(), wait3() or waitpid() returns due to a stopped or terminated
126 child process, the process ID of the child is returned to the calling
127 process. If there are no children not previously awaited, -1 is
128 returned with errno set to [ECHILD]. Otherwise, if WNOHANG is speci‐
129 fied and there are no stopped or exited children, 0 is returned. If an
130 error is detected or a caught signal aborts the call, a value of -1 is
131 returned and errno is set to indicate the error.
132
134 Wait() will fail and return immediately if:
135 [ECHILD] The calling process has no existing unwaited-for child
137 processes.
138 [EFAULT] The status or rusage arguments point to an illegal
140 address. (May not be detected before exit of a child
141 process.)
142 [EINTR] The call was interrupted by a caught signal, or the sig‐
144 nal had the SV_INTERRUPT flag set.
145
147 The wait and waitpid functions are defined by POSIX; wait4 and wait3
148 are not specified by POSIX. The WCOREDUMP macro and the ability to
149 restart a pending wait call are extensions to the POSIX interface.
150
152 exit(2) , sigvec(2) A wait function call appeared in Version 6 AT&T
153 UNIX.
1544th Berkeley Distribution March 12, 1993 WAIT(2)